Field of the Invention and Related Art Statement
The present invention generally relates to an optical data recording and retrieval technique, and more particularly to an apparatus for reading and/or writing a data signal with respect to an optical card.
The optical data recording and retrieval system has been described in many articles. For instance, in U.S. patent specification No. 4,634,850 there is disclosed the optical card read and/or write system. In such a system a quite large amount of data can be stored in a wallet-size card as optically readable pits. In general, on the card there are provided a number of tracks and each track is composed of a plurality of lines. A single data byte includes of a plurality of bits which are arranged in a direction Y perpendicular to a direction X in which the tracks extend. In order to read out the data stored on the card a light spot having such a diameter that all pits forming at least a single byte are simultaneously illuminated, and an image of an illuminated portion of the card is formed on a photodectector. The photodetector comprises an array of detectors which corresponds to an array of pits forming the single byte. Therefore, the data signal of the single byte can be read out simultaneously.
In the optical card reading and/or writing apparatus, a light beam is made incident upon the card generally along an inclined optical path and the reflected light is made incident upon the photodetector also along an inclined optical path. In FIG. 6 of the above mentioned U.S. patent specification No. 4,634,850 there is shown such an optical arrangement. Similar optical arrangements are also shown in Japanese Patent Application Laid-Open Publications (Kokai) Nos. 60-69836, 61-82286 and 61-208688. However, there references do not mention anything about focusing control or tracking control. In order to effect reading and writing in an accurate manner, it is necessary to perform focusing control and tracking control. Particularly, the card is usually carried by a user in his pocket so that the card is liable to be curved. Further, the card reading and/or writing apparatus should have a simple construction mainly due to the fact that its cost has to be reduced. Therefore, when the card is fed with respect to an optical head having a light source, photodetector and lenses, a distance between the card and head is liable to vary, so that focusing and tracking errors might be produced. Further, the feeding speed of the card might be varied and thus the data signal will not be derived accurately and will not be recorded at correct positions on the card. That is to say, it is difficult to make the feeding operation of the card synchronous with the reading and writing operation. In order to increase a data storage capacity of the card, it is necessary to effect focusing and tracking control, and to make the data reading and writing operation synchronous with the feeding of the optical card.